Spunbonded olefin sheet material is one material which is considered very desirable packaging material for numerous uses including envelopes, pouches, folders, sleeves, etc. Spunbonded olefin sheet material is relatively light in comparison to paper and other conventional packaging materials for its strength. One reason it is good for envelopes is its strength. Typically, paper weighing two to three times as much as spunbonded olefin sheet is required to provided comparable strength.
Many other features make it suitable for envelopes. The dense fiber network forming the sheet product offers extremely high resistance to tear, puncture and abrasion. Spunbonded olefin sheet has excellent resistance to water-borne soil and good resistance to degradation from age unless overly exposed to ultraviolet rays. It is inert to most acids and meets the requirements of the Federal Flame Fabrics Act. It is also unaffected by water or highly polar solvents and is therefore readily washable. Spunbonded olefin sheet is sold in different forms which have different characteristics in terms of tear strengths, tensile strengths, smoothness, porosity and flexibility and softness.
Hot-melt pressure sensitive adhesives are typically used with spun bonded olefin packages. The adhesive is applied directly to a package flap and a protective overlying release strip is applied as a protective cover. Such adhesives are very tenacious and stick firmly to the olefin sheet forming both the body and the flap. Because these adhesives are so tenacious, considerable force is required to separate the flap from body of the envelopes on which they are applied. This opening of the packages can be very difficult.
Typically, the opening of such a package results in a partial tearing away of filaments from the surface of olefin sheet and an extension from the surface of the olefin of the partially torn filaments. Additionally, some filaments are usually torn completely away from the surface of the olefin and adhered to the adhesive of the flap of the package. Furthermore, there is usually some stretching and wrinkling of the olefin material forming at least the flap of the package in the region of the adhesive. If an attempt is made to reseal such a package after an initial opening, the stretching and wrinkling of the flap and the relative ease with which the flap reopens due to the partial covering of the adhesive with broken olefin filaments provide a means by which it can be readily determined that the package was previously opened and resealed. Thus, olefin packages using hot-melt pressure sensitive adhesives were inherently tamper evident.
More easily opening closure systems using spunbonded olefin have been used as resealable packaging systems. One approach to making the resealable envelopes formed of this material was the use of mating flexible fabric fasteners such as Velcro.RTM.-type fastening members. The non-mating sides of these fastening members were permanently adhered to a body portion of an olefin packaging and to a flap or other closure portion of the olefin packaging. The engageable sides of the fabric fastening members matingly faced one another. However, this type of closure tends to be too thick, heavy and costly. Additionally, since this type of closure is not altered by the act of opening and closing, it is not tamper evident.
Another system for sealing envelopes formed of this material includes the use of identical polymer patches each bearing an identical adhesive on one side thereof which bonds well to both the olefin and to a polymer carrier carrying the adhesive. A first patch is applied to one surface of the packaging while a second patch is applied to the flap over an opening through the flap which overlies the first patch when the flap is applied to the one surface of the package. The opening through the flap is significantly smaller than the overall size of the patch applied to the flap. This insures that an adequate area of the flap is provided to secure the second patch and presents less than half of the adhesive surface of the second patch to engage with the underlying first patch mounted on the surface. In this way, a weaker bond is created between the second patch on the panel and the first patch on the packaging surface than is created between the second patch on the panel and the panel or between the first patch and the packaging surface. While this type of double patch system is useful in application requiring a number of opening and resealing operations, it too is not tamper evident.
It would be very desirable to provide permanently sealable yet easily openable packaging. Additionally, it would be desirable to provide easily openable packaging which is tamper evident.